1. Field of the Invention
This invention relates to a novel strain of Agrobacterium radiobacter and, more particularly, to a heteropolysaccharide produced from such novel strain.
This invention further relates to oil recovery and, more particularly, to a gel-forming polysaccharide biopolymer which, when injected into an oil reservoir formation, enhances the oil recovery therefrom.
2. Information Disclosure Statement
In the recovery of oil from petroleum reservoirs, water flooding is a common practice used to increase the volume of oil recovered from a reservoir formation. Frequently, however, water will bypass oil-rich regions of the reservoir by travelling through layers of higher permeability. This process results in a lower oil recovery and higher production of water than is economical. Profile modification has become a popular technique for improving the efficiency of oil recovery by water flooding. By introducing a water-based, low permeability gel into the high permeability zones described, injected water is redirected toward oil-rich, underswept regions of the reservoir thereby improving oil recovery.
Commercially available profile modification systems usually employ water-soluble polymers cross-linked with Cr.sup.3+ or Al.sup.3+ cations to yield gels "in situ" in the reservoir formation. These polymers are, generally, synthetic hydrolyzed polyacrylamides or xanthan gum, a polysaccharide biopolymer. The latter molecule enjoys an advantage in that it is more tolerant to Na.sup.+ and Ca.sup.++ ions frequently found in reservoir fluids. This biopolymer is limited, however, to relatively low temperature oil fields. For example, xanthan gels crosslinked with C.sup.3+ readily degrade in a temperature range of 60.degree.-90.degree. C. by a process known as syneresis (gel compaction coupled with water expulsion). Profile modification systems and processes are described by Abdo et al, in "Field Experience with Floodwater Diversion by Complexed Biopolymers", SPE/DOE 12642, presented at the SPE/DOE Fourth Symposium on Enhanced Oil Recovery held at Tulsa, OK, April 15-19, 1984 (using Pfizer "FLOCON 4800," based on a xanthan gum) and by Chang et al, in "Laboratory Studies and Field Evaluation of a New Gelant for High-Temperature Profile Modification", SPE 14235, presented at the 60th Annual Technical Conference of the Society of Petroleum Engineers held in Las Vegas, NV, September 22-25, 1985 (using Pfizer's "FLOPERM.TM." 325, based on synthetic, thermosetting materials).
Water flooding is a common practice in oil recovery to increase the amount of oil obtained from a reservoir. Polymer flooding utilizes a viscosifying polymer to increase the efficiency of a water flood. Microbial heteropolysaccharides have been shown to be useful in this instance and xanthan gum has been most often used (see "Economic Value of Biopolymers and their Use in Enhanced Oil Recovery" by A. Gabriel, pages 191-204, in Microbial Polysaccharides and Polysaccharases. R. C. W. Berkely, G. W. Gooday and D. C. Ellsoods, eds, Academic Press, 1979). Various Agrobacterium radiobacter strains have been shown to produce heterpolysaccharides. For example, U.S. Pat. No. 4,259,451 discloses a culture of a variant strain of A. radiobacter, Accession No. ATCC 31643. U.S. Pat. No. 4,269,939 discloses a process for producing a heteropolysaccharide by bacterial fermentation of an organism deposited under Accession No. ATCC 31643, and U.S. Pat. No. 4,634,667 discloses a culture of a variant strain of A. radiobacter assigned Accession No. NCIB 11883 by the National Collection of Industrial Bacteria (U.K.).
U.S. Pat. No. 4,647,657 discloses a heterpolysaccharide prepared by the fermentation of a Flavobacterium species ATCC 53201 which has properties of a viscosity control agent in aqueous systems.
U.S. Pat. No. 4,738,727 discloses aqueous solutions of a heteropolysaccharide comprising glucose, galactose, pyruvic and succinic acid.
U.S. Pat. No. 4,640,358 discloses a process for oil recovery wherein is used a thickening agent, i.e., a polyvalent metal ion complex of a fungal polysaccharide, a scleroglucan, to improve the oil recovery.
U.S. Pat. No. 4,347,146 discloses the employment of a poly(glucosylglucan) as a thickening agent for an aqueous driving fluid in a process for producing petroleum from a petroleum-bearing subterraneon formation.